If typer phase is defined then perform member lookup of a symbol
sym at typer phase.

If typer phase is defined then perform member lookup of a symbol
sym at typer phase. This method results from refactoring. The
original author of the logic that uses typer phase didn't explain
why we need to force infos at that phase specifically. It only mentioned
that ClassfileParse can be called late (e.g. at flatten phase) and
we make to make sure we handle such situation properly.

Note: these methods are different from the methods of the same name found
in Definitions.

Note: these methods are different from the methods of the same name found
in Definitions. These test whether a symbol represents one of the boxTo/unboxTo
methods found in BoxesRunTime. The others test whether a symbol represents a
synthetic method from one of the fake companion classes of the primitive types,
such as Int.box(5).